SUMMARY The Gordon Research Conference on Mammary Gland Biology (GRC MGB) and the highly successful Gordon Research Seminar (GRS) that accompanies this meeting are unique amongst breast cancer conferences as they bring together a very diverse mix of scientists and clinician-scientists interested in the molecular and cellular mechanisms that govern normal mammary gland development, normal physiology, tumor initiation and progression and metastasis. There is a strong focus on breast cancer prevention and treatment (based on elucidating the early and later events that contribute to breast cancer onset and progression) and emerging `cutting edge' science relevant to the field. The Mammary Gland Biology GRC/GRS is the only conference focused on harnessing insights from normal mammary gland biology to understand events that give rise to breast cancer and has become a `must attend' for mammary gland biologists and cancer researchers (particularly in basic and translational research areas). The Specific Aims of the 2019 GRC/GRS are to deliver a program that addresses key scientific questions and controversies for the field. The 2019 conference will focus on recent discoveries and outstanding questions in the mammary gland biology field that have immediate and long-term relevance to breast cancer prevention and treatment. International experts are being invited to address the following topics: (1) Stem Cell Regulation and Development, (2) Immune Regulation of Development and Disease, (3) Epithelial Morphogenesis and Functional Differentiation, (4) Stromal Regulation of Epithelial Plasticity, (5) Breast Cancer and the Environment, (6) Transcriptional and Translational Regulation of Development and Cancer (7) Metabolism and Epigenetic Regulation, (8) Emerging Models of Mammary Gland Development and Cancer, (9) Future Directions in Mammary Gland Research.